mm: a few small updates for radix-swap

Remove PageSwapBacked (!page_is_file_cache) cases from
add_to_page_cache_locked() and add_to_page_cache_lru(): those pages now
go through shmem_add_to_page_cache().

Remove a comment on maximum tmpfs size from fsstack_copy_inode_size(),
and add a comment on swap entries to invalidate_mapping_pages().

And mincore_page() uses find_get_page() on what might be shmem or a
tmpfs file: allow for a radix_tree_exceptional_entry(), and proceed to
find_get_page() on swapper_space if so (oh, swapper_space needs #ifdef).

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 232eb2736a79..b40ac6d4e86e 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -336,6 +336,14 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
         unsigned long count = 0;
         int i;
 
+        /*
+         * Note: this function may get called on a shmem/tmpfs mapping:
+         * pagevec_lookup() might then return 0 prematurely (because it
+         * got a gangful of swap entries); but it's hardly worth worrying
+         * about - it can rarely have anything to free from such a mapping
+         * (most pages are dirty), and already skips over any difficulties.
+         */
+
         pagevec_init(&pvec, 0);
         while (index <= end && pagevec_lookup(&pvec, mapping, index,
                         min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {